Radiation detector array using radiation sensitive bridges

Abstract

An infrared (IR) simulator is disclosed in which an array of pixels is defined on an insulative substrate by resistor bridges which contact the substrate at spaced locations and are separated from the substrate, and thereby thermally insulated therefrom, between the contact locations. Semiconductor drive circuits on the substrate enable desired current flows through the resistor bridges in response to input control signals, thereby establishing the appropriate IR radiation from each of the pixels. The drive circuits and also at least some of the electrical lead lines are preferably located under the resistor bridges. A thermal reflector below each bridge shields the drive circuit and reflects radiation to enhance the IR output. The drive circuits employ sample and hold circuits which produce a substantially flicker-free operation, with the resistor bridges being impedance matched with their respective drive circuits. The resistor bridges may be formed by coating insulative base bridges with a resistive layer having the desired properties, and overcoating the resistive layers with a thermally emissive material. The array is preferably formed on a silicon-on-sapphire (SOS) wafer. Arrays of electromagnetic radiation bridge detectors may also be formed, with the bridges having either resistor, thermocouple or Schottky junction constructions.

We claim: 
     
       1. A two-dimensional sensing array for electromagnetic radiation (emr), comprising: a substrate,   an array of emr detector cells in said substrate, each of said cells including an emr sensitive bridge structure spanning a portion of the cell, said bridge structure being shaped to form a generally thermally insulative gap between the bridge structure and substrate, and having a defined characteristic which varies in accordance with the amount of emr received by the bridge, and   means for monitoring said defined characteristic for each of said cells.   
     
     
       2. The emr sensing array of claim 1, said bridge structures comprising respective resistor bridges. 
     
     
       3. The emr sensing array of claim 2, said resistor bridges comprising a center span having a target area for receiving emr and a plurality of support legs elevating the center span above the substrate, the geometries of said center span and support legs being selected to enhance emr absorption by the center span relative to thermal losses from the center span to the substrate through the support legs. 
     
     
       4. The emr sensing array of claim 3, wherein the cross-sectional areas of said support legs are substantially less than the areas of their respective target areas to thermally insulate the center span from the substrate. 
     
     
       5. The emr sensing array of claim 4, wherein a pair of support legs are provided for each center span, generally centered on opposite sides of the support span. 
     
     
       6. The emr sensing array of claim 4, said center spans generally comprising rectangles, wherein a support leg is provided adjacent each corner of said rectangles. 
     
     
       7. The emr sensing array of claim 3, said center spans having a generally serpentine configuration to increase their effective lengths and reduce thermal conduction losses therefrom. 
     
     
       8. The emr sensing array of claim 2, said monitoring means comprising respective resistors connected in series with the resistor bridges to form respective voltage divider circuits, means for applying a voltage to said voltage divider circuits, and means for monitoring the voltages across said resistors as a function of the emr received by said resistor bridges. 
     
     
       9. The emr sensing array of claim 8, said monitoring means comprising respective monitoring circuits at each cell, said monitoring circuits including multiple-stage amplifier readout circuits to reduce Johnson noise associated with said voltage divider circuits. 
     
     
       10. The emr sensing array of claim 2, said monitoring means including respective monitoring circuits at each cell, said resistor bridges comprising a center span having a target area for receiving emr, a plurality of support legs elevating the center span above the substrate, and a thin layer of conductive material on said support legs electrically connecting said center span to said monitoring circuits, said layers of conductive material being thin enough to substantially maintain the thermal isolation of said center spans form the substrate. 
     
     
       11. The emr sensing array of claim 2, said resistor bridges being formed from an amorphous semiconductor material. 
     
     
       12. The emr sensing array of claim 1, said bridge structures comprising respective junction devices having an electrical characteristic which varies in accordance with the amount of emr received by the junction device, and said monitoring means comprises means for monitoring said electrical characteristic for each of said cells. 
     
     
       13. The emr sensing array of claim 12, said junction devices comprising junctions of unlike materials selected to generate a thermally induced voltage, said junction devices being configured to heat in response to applied emr within a desired range of wavelengths, and said monitoring means comprises means for sensing thermally induced voltages in each of said junction devices. 
     
     
       14. The emr sensing array of claim 13, said junction devices comprising semiconductor-metal junctions. 
     
     
       15. The emr sensing array of claim 14, said junction devices comprising a stacked plurality of alternating semiconductor and metal layers. 
     
     
       16. The emr sensing array of claim 13, said monitoring means comprising respective resistors connected in series with said junction devices to form respective voltage divider circuits, means for applying a voltage to said voltage divider circuits, and means for monitoring the voltages across said resistors as a function of the emr received by said junction devices. 
     
     
       17. The emr sensing array of claim 12, said junction devices comprising Schottky diode bridge structures, and said monitoring means comprises means for reverse biasing said Schottky diode bridge structures and monitoring their leakage currents as a function of emr-induced heating. 
     
     
       18. The emr sensing array of claim 17, said Schottky contact bridge structures comprising adjacent layers of a semiconductor with a metal or doped semiconductor conductor, said layers meeting along a Schottky contact junction. 
     
     
       19. The emr sensing array of claim 18, wherein said semiconductor is amorphous germanium or amorphous tin. 
     
     
       20. The emr sensing array of claim 1, said emr sensitive bridge structures including a layer of emr absorbing material for receiving emr and activating the remainder of the bridge structures to vary said defined characteristic in response to emr received by said absorbing material. 
     
     
       21. The emr sensing array of claim 1, said monitoring means including a readout circuit for each cell situated on the substrate at least partially under the bridge structure for that cell and at least partially shaded thereby from applied emr. 
     
     
       22. The emr sensing array of claim 21, said monitoring means including actuating and monitoring lead lines extending along the substrate for respectively actuating the bridge structures response to received emr and monitoring said responses, at least some of said lines extending under at least some of said bridge structures. 
     
     
       23. The emr sensing array of claim 1, further including a lens for imaging an emr source onto said array. 
     
     
       24. The emr sensing array of claim 1 wherein said means for monitoring further includes compensating means comprising: shutter means, placed in font of the detector arry for periodic closure to obtain black readouts, and   storage means positioned to receive said black readouts and provide compensation for subsequent readouts with the shutter open.   
     
     
       25. An emr detector, comprising: a substrate,   an emr bridge structure spanning a portion of said substrate and separated therefrom by a generally thermally insulative gap, said bridge structure having a defined characteristic which varies in accordance with the amount of emr which it receives,   means for elevating the bridge structures above the substrate, and   means for monitoring said defined characteristic.   
     
     
       26. The emr detector of claim 25, said bridge structure comprising a resistor bridge. 
     
     
       27. The emr detector of claim 26, said bridge structure and elevating means comprising a center span having a target area for receiving emr and a plurality of support legs elevating the center span above the substrate, the geometries of said center span and support legs being selected to enhance emr absorption by the center span relative to thermal losses from the center span to the substrate through the support legs. 
     
     
       28. The emr detector of claim 27, wherein the cross-sectional areas of said support legs are substantially less than the target area of said target area to thermally insulate the center span from the substrate. 
     
     
       29. The emr detector of claim 28, wherein a pair of support legs are provided for the center span, generally centered on opposite sides of the support span. 
     
     
       30. The emr detector of claim 28, said center span generally comprising a rectangle, wherein a support leg is provided adjacent each corner of said rectangle. 
     
     
       31. The emr detector of claim 27, said center span having a generally serpentine configuration to increase its effective length and reduce thermal conduction losses therefrom. 
     
     
       32. The emr detector of claim 27, said monitoring means including a monitoring circuit on the substrate, and further comprising a thin layer of conductive material on said support legs electrically connecting said center span to said monitoring circuit, said layers of conductive material being thin enough to substantially maintain the thermal isolation of said center span from the substrate. 
     
     
       33. The emr detector of claim 26, said monitoring means comprising a resistor connected in series with the resistor bridge to form a voltage divider circuit, means for applying a voltage to said voltage divider circuit, and means for monitoring the voltage across said resistor as a function of the emr received by the resistor bridge. 
     
     
       34. The emr detector of claim 33, said monitoring means including a multiple-stage amplifier readout circuit to reduce Johnson noise associated with said voltage divider circuit. 
     
     
       35. The emr detector of claim 26, said resistor bridge being formed from an amorphous semiconductor material. 
     
     
       36. The emr detector of claim 25, said bridge structure comprising a junction device having an electrical characteristic which varies in accordance with the amount of emr received by the junction device, and said monitoring means comprises means for monitoring said electrical characteristic. 
     
     
       37. The emr detector of claim 36, said junction device comprising a junction of unlike materials selected to generate a thermally induced voltage and configured to heat in response to applied emr within a desired range of wavelengths, and said monitoring means comprises means for a thermally induced voltage in said junction device. 
     
     
       38. The emr detector of claim 37, said junction device comprising a semiconductor-metal junction. 
     
     
       39. The emr detector of claim 38, said junction device comprising a stacked plurality of alternating semiconductor and metal layers. 
     
     
       40. The emr detector of claim 37, said monitoring means comprising a resistor connected in series with said junction device to form a voltage divider circuit, means for applying a voltage to said voltage divider circuit, and means for monitoring the voltage across said resistor as a function of the emr received by the junction device. 
     
     
       41. The emr detector of claim 36, said junction device comprising a Schottky diode bridge structure, and said monitoring means comprises means for reverse biasing said Schottky diode bridge structure and monitoring its leakage current as a function of emr-induced heating. 
     
     
       42. The emr detector of claim 41, said Schottky contact bridge structure comprising adjacent layers of a semiconductor with a metal or doped semiconductor conductor, said layers meeting along a Schottky contact junction. 
     
     
       43. The emr detector of claim 42, wherein said semiconductor is amorphous germanium or amorphous tin. 
     
     
       44. The emr detector of claim 25, said emr sensitive bridge structure including a layer of emr absorbing material for receiving emr and activating the remainder of the bridge structures to vary said defined characteristic in response to emr received by said absorbing material. 
     
     
       45. The emr detector of claim 25, said monitoring means including a readout circuit situated on the substrate at least partially under said bridge structure and at least partially shaded thereby from applied emr. 
     
     
       46. The emr detector of claim 25 wherein said means for monitoring further includes compensating means comprising: shutter means, placed in front of the detector array for periodic closure to obtain black readouts, and   storage means positioned to receive said black readouts and provide compensation for subsequent readouts with the shutter open.